The present invention relates to a hydrostatic transmission for use in a vehicle and, more particularly, the present invention relates to a hydrostatic transmission with an integral actuator.
It is common in the prior art to propel a vehicle with a hydrostatic transmission. An output shaft of a vehicle engine is coupled to a shaft of a pump of a hydrostatic transmission. The pump is typically encased in a hydrostatic transmission housing and is at least partially submerged in a bath of hydrostatic fluid. Rotation of the shaft of the pump by the motor output shaft produces a flow of hydrostatic fluid from the pump. The flow of hydrostatic fluid from the pump is coupled to a hydrostatic motor which propels one or more of the wheels of the vehicle. The flow of the hydrostatic fluid from the pump to the hydrostatic motor is regulated to control the speed and direction of rotation of the one or more drive wheels of the vehicle.
U.S. Pat. No. 4,878,338 to Aldred et al. discloses a grass cutting machine that includes an A-frame chassis supported by two front wheels and a rear wheel. The chassis carries a conventional diesel engine which provides the traction drive for the machine through front wheels via a hydrostatic transmission. U.S. Pat. No. 5,518,079 to Zvolanek discloses a lawn mower having an engine that is coupled to left and right pumps that correspond to left and right rear wheels of the lawn mower. The left and right pumps produce a flow of fluid that is communicated to left and right wheel motors. Selective control of the fluid from the left and right pumps to the left and right wheel motors controls the movement of the lawn mower.
It is also known in the prior art to drive cutting blades of a mowing unit with hydraulic fluid. For example, U.S. Pat. No. 5,133,174 to Parsons, Jr. discloses the rotation of pumps in fluid pumping units with a power take-off of a tractor to produce fluid pressure. The pressure generated by the fluid pumping units is selectively communicated to fluid drive motors by solenoid valves. The fluid drive motors drive the cutters of the mowing unit. The driver of the mowing unit may actuate one or more of the solenoid valves to actuate one or more of the cutters of the mowing unit.
U.S. Pat. No. 4,178,741 to Lonn et al. discloses a riding mower having a propulsion means, a seat for the operator and at least one cutting head that is hydraulically driven. The cutting head is controllable between an operating norm and a non-operating norm by means of a hydraulic valve having two movable spools, and the cutting head is movable between a cutting position and a transport position by means of a hydraulic cylinder. A solenoid valve is employed to control one of the movable spools.
U.S. Pat. No. 4,878,338 to Aldred et al. describes a grass cutting machine with two forward cutting units of the reel type supported from the chassis on respective support arms, each pivotally mounted with respect to the chassis on an axle. Each cutting unit is provided with a hydraulic drive motor that receives hydraulic fluid through lines.
It is also known in the prior art to selectively engage a power take-off using a vacuum actuator. For example, U.S. Pat. No. 5,918,449 to Rush et al. discloses a control system for controlling an associated device that includes a vacuum actuator, a connecting means for operatively connecting the vacuum actuator to the associated device, a vacuum means for providing a vacuum to the vacuum actuator, and activating means for selectively electrically activating the vacuum actuator. To engage an associated PTO shaft, an operator switches an electric switch,, opening a control valve and activating a vacuum actuator. Next, a clutch arm is pivoted, causing a braking arm to take a PTO pulley out of breaking engagement and forcing an idler pulley into operative engagement with the PTO belt. This connects the PTO pulley with a drive pulley thereby rotating the PTO shaft. When the PTO is to be disengaged, the brake arm is effective to stop the motion of the implement driven by the PTO, and to stop the implement within a very short time.
The present invention concerns a hydrostatic transmission with an integral actuator for a vehicle having an engine or motor and a frame. The hydrostatic transmission with integral actuator includes a transmission housing that is connected to the vehicle frame. A transmission shaft that is adapted to be coupled to an output of the engine extends into the transmission housing. First and second pumps disposed in the housing are connected to the shaft. Rotation of the shaft produces a flow of fluid from each of the first and second pumps. The flow of fluid from the first pump is used to propel the vehicle. An actuator is at least partially contained within the housing and is coupled to the second pump. A valve is operably connected to either the second pump or the actuator or both the second pump and the actuator. Operation of the valve selectively communicates fluid pressure to the actuator to extend and retract the actuator.
The hydrostatic transmission with integral actuator may include a spring connected to the actuator that biases the actuator to a first position when the valve is closed. The spring may be enclosed in the housing of the actuator or may be external to a housing of the actuator. The valve, which may be a solenoid valve, may be enclosed in the transmission housing.
The integral actuator is extended and retracted by coupling the transmission shaft to the engine. The transmission shaft is coupled to a pump to create fluid pressure in the pump. Fluid pressure is selectively communicated from the pump to the integral actuator to selectively extend and retract a portion of the integral actuator that extends from the transmission housing. The pressure is selectively communicated from the pump to the integral actuator by opening a valve. The integral actuator of a first embodiment is extended by communicating fluid pressure to the integral actuator. An integral actuator of a second embodiment is retracted by communicating fluid pressure to the integral actuator.
The hydrostatic transmission with integral actuator may be used to engage a PTO shaft. A vehicle having a body, an engine, a hydrostatic transmission with an integral actuator, and a PTO shaft, is provided. Fluid pressure is selectively communicated to the integral actuator to engage the PTO shaft. A connector link may be connected to the integral actuator and operably connected to a PTO, such that movement of the integral actuator from a first position to a second position engages the PTO.
The hydrostatic transmission with integral actuator provides a cost effective means for controlling a variety of implements of a lawn and garden tractor. The self-contained nature of the actuator of the hydrostatic transmission increases the life of the actuator, since those portions of the actuator within the transmission housing are not exposed to the environment. The internal actuator of the hydrostatic transmission eliminates the need for hoses that carry hydrostatic fluid from a source of hydrostatic fluid to a distant external actuator. The implements of a lawn and garden tractor may be conveniently connected to the integral actuator by linkages or cables.
Additional features of the invention will become apparent and a fuller understanding will be obtained by reading the following detailed description in connection with the accompanying drawings.